The present invention relates to a cold rolled steel sheet which has excellent corrosion resistance to sulfuric acid. More specifically, the present invention relates to a cold rolled steel sheet having excellent corrosion resistance to sulfuric acid, which is used as the material of the components exposed to sulfuric acid, such as the pre-heater of a thermoelectric power plant, boiler components and the like.
Generally, it is known that a large amount of Cu is added in a sulfuric acid corrosion resistant steel so that corrosion of the sulfuric-acid-resistant steel can be slowed down under sulfuric acid atmosphere. However, although Cu is superior in slowing down sulfuric acid corrosion compared with other additives, if too much is added, problems occur, such as the generation of cracks and the like during hot rolling.
Japanese Patent Application Laid-open No Hei-9-25536 discloses an acid-corrosion resistant steel which aims at solving the above described problem. This steel includes in weight %: 0.01xcx9c0.15% of C, 0.1xcx9c0.5% of Si, 0.1xcx9c0.5% of Mn, 0.03% or less of P, 0.01% or less of S, 0.2xcx9c1.0% of Cu, 0.5% or less of Ni, 2.0% or less of Cr, 0.1% or less of Al, 0.01xcx9c1.0% of Sn and/or Sb, 0.005% or less of B, 0.2% or less of V, Nb: 0.2% or less of Nb, and 0.02% or less of Ti.
Another example is Japanese Patent Application Laid-open No Hei-10-110237 which includes in weight %: 0.01xcx9c0.15% of C, 0.1xcx9c0.5% of Si, 0.1xcx9c0.5% of Mn, 0.03% or less of P, 0.005% or less of S, 0.2xcx9c1.0% of Cu, 0.5% or less of Ni, 2.0% or less of Cr, 0.1% or less of Al, 0.2% or less of V, 0.2% or less of Nb, 0.2% or less of Ti, one selected from among 0.01xcx9c1.0% of Sn and/or Sb, 0.001xcx9c0.01% of B, and 0.01xcx9c0.5% of Mo, and a balance of Fe and other unavoidable impurities.
That is, in the above described invention, a proper amount of Cu is added and at the same time, other elements are compositely added. Thus a superior acid-corrosion resistance is aimed to be achieved, but at a low temperature and a low sulfuric acid concentration, the corrosion rate is still high, this being the problem.
In order to solve the above described problems, the present inventors carried out research and experiments repeatedly, and the result is the present invention.
Therefore it is an object of the present invention to provide a cold rolled steel sheet with an excellent sulfuric acid corrosion resistance, in which not only Cu but also a proper amount of Co is added so that the corrosion rate can be greatly lowered at a low temperaturexe2x80x94low sulfuric acid concentration, thereby providing a cold rolled steel having a superior corrosion resistance against sulfuric acid.
In achieving the above object, the cold rolled steel sheet with an excellent sulfuric acid corrosion resistance according to the present invention includes in weight %: 0.15% or less of C, 1.0% or less of Si, 0.2xcx9c1.5% of Mn, 0.03% or less of S, 0.03% or less of P, 0.01xcx9c0.1% of Al, 0.2xcx9c1.0% of Cu, 0.02xcx9c0.2% of Co, and a balance of Fe and other unavoidable impurities.